This application claims the benefit of Japanese Application 2001-019,487, filed Jan. 29, 2001, the entirety of which is incorporated herein by reference.
(1) Field of the Invention
The present invention relates to an electrostatic chuck which can achieve a uniform temperature distribution of a wafer and suppress a particle generation.
(2) Related Art Statement
At present, electrostatic chucks are used for attracting and holding semiconductor wafers in finely working e.g., transferring, exposing, film-forming by CVD, washing, etching, and dicing the semiconductor wafers. Normally, a plurality of projecting portions or embossed portions protruded from a mount plane of an insulation layer, and crown planes (contact planes) of the projecting portions are contacted to the semiconductor wafer. Moreover, DC voltage is applied to an inner electrode in the insulation layer, and Johnson-Rahbeck force is generated at a contact boundary between the semiconductor wafer and the projecting portions, so that the semiconductor wafer is attracted on the contact planes. Therefore, if an area of contact planes (crown planes) is increased, it is possible to improve an attraction of the semiconductor wafer.
Further, in order to perform predetermined processes such as film-forming and so on with respect to the semiconductor wafer, it is necessary to maintain a temperature of the semiconductor wafer at a constant temperature and to make a temperature at respective portions of the semiconductor wafer uniform. In this case, if a temperature of the insulation layer of the electrostatic chuck is increased by a built-in heater and so on, a heat is conducted from the insulation layer to the semiconductor wafer at a contact region between the contact planes of the projecting portions and a rear plane of the semiconductor wafer. However, in the method mentioned above, since a contacting state between the projecting portions and the semiconductor wafer is varied in accordance with a slight hardness variation of the contact planes of the projecting portions or a concavo-convex variation of a plane surface, a heat contacting resistance is varied at respective contact planes of respective projecting portions. Therefore, a heat from the insulation layer cannot be conducted stably to the overall semiconductor wafer, and thus a temperature uniformity of the semiconductor wafer is liable to be decreased. In order to eliminate such a drawback, there is proposed a method wherein a backside gas with a constant pressure is flowed through a space between the rear plane of the semiconductor wafer and the insulation layer, and a heat from the insulation layer is conducted to the semiconductor wafer by utilizing a heat radiation and a heat convection from the backside gas. In this case, if a pressure of the backside gas becomes larger, such tendencies are detected that, a heat conduction from the insulation layer to the semiconductor wafer becomes larger, and a temperature uniformity of the semiconductor wafer can be improved.
However, if the area of the contact planes of the projecting portions is made larger so as to improve an attraction of the semiconductor wafer, the rear plane of the semiconductor wafer and the contact planes of the projecting portions are rubbed, so that particles are generated and deposited on the contact planes of the projecting portions, and further, there is a possibility such that they are adhered to the semiconductor wafer.
On the other hand, if an area of the contact planes of the projecting portions is made smaller, a particle generation is decreased and thus an adhesion of particles to the projecting portions is decreased. However, in this case, since Johnson-Rahbeck force acting between the contact planes and the semiconductor wafer is decreased, an attraction force of the semiconductor wafer is also decreased.
Further, when the backside gas with a predetermined pressure flows between the rear plane of the semiconductor wafer and the insulation layer, an ascending force due to the backside gas is applied to the semiconductor wafer. Therefore, an attraction force actually acting on the semiconductor wafer becomes such a value that the ascending force acting from the backside gas to the semiconductor wafer is taken from an attraction force due to electrostatic effects acting from the electrostatic chuck to the semiconductor wafer. In this case, if an area of the contact planes of the projecting portions is decreased as mentioned above the ascending force acting to the semiconductor wafer becomes relatively larger, and thus the attraction force of the semiconductor wafer is not sufficient. In order to eliminate such a drawback, if the pressure of the backside gas is made smaller, heat conduction due to the backside gas becomes insufficient, and thus a temperature uniformity of the semiconductor wafer is deteriorated.
An object of the present invention is to provide an electrostatic chuck having projecting portions protruded from a wafer mount plane, wherein a backside gas is flowed in a space defined by the wafer mount plane, the projecting portions and the wafer under such a condition that the wafer is attracted to the wafer mount plane so as to maintain the temperature uniformity of the wafer, which can reduce particles generated by rubbing between the projection portions and the wafer and improve the temperature uniformity of the wafer.
According to the invention, an electrostatic chuck having an insulation layer including a mount plane on which a wafer is mounted, an inner electrode provide in the insulation layer, and projecting portions protruded from the mount plane which include contact planes to be contacted to the wafer, wherein a backside gas is flowed in a space defined by the mount plane, the projecting portions, and the wafer under such a condition that the wafer is attracted to the mount plane so as to maintain a temperature uniformity of the wafer, comprises a construction such that a total amount of areas of the contact planes of the projecting portions is not less than 5% and not more than 10% with respect to an area of the inner electrode, and heights of the projecting portions are not less than 5 xcexcm and not more than 10 xcexcm.
Moreover, according to the invention, a substrate processing apparatus wherein a predetermined process is applied to a plane of a substrate, comprises: a process chamber in which the predetermined process is performed; the electrostatic chuck used for electrostatically attracting and holding the substrate at a predetermined position in the process chamber; and a power source for attracting.
The present inventors found the following and achieved the present invention. That is, even in the case such that a total amount of areas of the contact planes of the projecting portions to be contacted to the wafer is made smaller to a level of not more than 10% with respect to an area of the inner electrode so as to reduce particle generations, if heights of the projecting portions are controlled to not less than 5 xcexcm and not more than 10 xcexcm, it is possible to effectively perform heat conduction through the backside gas from the electrostatic chuck to the semiconductor wafer, and thus, it is possible to maintain high temperature uniformity for the semiconductor wafer.
This is further explained. Generally, a height of the projecting portion of the electrostatic chuck was about 20 xcexcm, and heat was conducted by heat convection between the insulation layer and the semiconductor wafer. Therefore, it was thought that a low height of the projecting portion is not effective upon a heat conduction.
However, it was understood that, if a height of the projecting portion is controlled actually to 5-10 xcexcm, it is effective upon a heat conduction from another point of view. That is, it was assumed that coulomb force is acted between electric charges suspended near a plane of the insulation layer and electrostatic charges of the semiconductor wafer, other than an attraction force due to Johnson-Rahbeck force at a contact region between the projecting portions and the semiconductor wafer. Therefore, it was understood that an electrostatic attraction force of the semiconductor wafer is not decreased as expected. As a result, a pressure of the backside gas between the rear plane of the semiconductor wafer and the mount plane is made larger, and a heat conduction through the backside gas is effectively performed, so that it is possible to achieve a uniform temperature distribution of the semiconductor wafer. In order to obtain such advantages, it is necessary to set a height of the projecting portion to not more than 10 xcexcm. From this point of view, it is more preferred to set a height of projecting portion to not more than 8 xcexcm.
Moreover, it was understood that, if a height of the projecting portion is made smaller, a contribution of coulomb force mentioned above becomes larger, and an electrostatic attraction force is further improved. However, in the case such that a height of the projecting portion becomes less than 5 xcexcm, a heat conduction efficiency was decreased even if a pressure of the backside gas was made larger, and thus a temperature uniformity of the semiconductor wafer was decreased. Assumably, it was understood that, if a height of the projecting portion becomes less than 5 xcexcm, a heat convection is not contributed and thus a heat conduction is mainly performed by a heat radiation. Moreover, it is understood that, since the particles on the mount plane are not directly contacted to the semiconductor wafer but are attracted electrostatically to the semiconductor wafer, it is difficult to reduce the particles from the semiconductor wafer. From this point of view, it is further preferred to set a height of the projecting portion to not less than 6 xcexcm.
Further, if a total amount of areas of the contact planes of the projecting portions to be contacted to the wafer is less than 5% with respect to an area of the inner electrode, an attraction force is lowered excessively even with taking into consideration of a contribution of coulomb force mentioned above, and thus it is not possible to flow the backside gas with a sufficiently high pressure, so that a temperature uniformity of the semiconductor wafer is decreased.
From the above point of view, it is further preferred to set a total amount of areas of the contact planes of the projecting portions to be contacted to the wafer to not more than 8% and not less than 6% with respect to an area of the inner electrode.
An area of the contact plane of the projecting portion to be contacted to the wafer means an area contacting to the rear plane of the wafer during a normal wafer attracting state. This is normally equal to an area of a top plane of the projecting portion. In this case, if some projecting portions have a low height and they are not contacted to the rear plane of the wafer during a normal wafer mounting state, top planes of those projecting portions are not included in this area.
Moreover, both of an area of the inner electrode and an area of the contact plane of the projecting portion means the area measured from a vertical direction with respect to the mount plane.
A height of the projecting portion is measured by a dial-gauge or a three-dimensional shape measuring apparatus.
The kinds of processes with respect to the substrate are not limited, but mention may be made of finely working e.g., transferring, exposing, film-forming by CVD, washing, etching, and dicing the semiconductor wafers.
The kind of substrate is not limited, but it is preferred to use a semiconductor wafer.
As the chamber and the power source for electrostatically attracting, use may be made of the known members in their technical fields.